JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 110, A08212, doi:10.1029/2005JA011188, 2005

An obliquely propagating electromagnetic drift instability in the lower hybrid frequency range

Hantao Ji and Russell Kulsrud
Center for Magnetic Self-Organization in Laboratory and Astrophysical Plasmas, Plasma Physics Laboratory, Princeton, New Jersey, USA

William Fox
Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusettes, USA

Masaaki Yamada
Center for Magnetic Self-Organization in Laboratory and Astrophysical Plasmas, Plasma Physics Laboratory, Princeton, New Jersey, USA

Abstract

By employing a local two-fluid theory, we investigate an obliquely propagating electromagnetic instability in the lower hybrid frequency range driven by cross-field current or relative drifts between electrons and ions. The theory self-consistently takes into account local cross-field current and accompanying pressure gradients. It is found that the instability is caused by reactive coupling between the backward propagating whistler (fast) wave in the electron frame and the forward propagating sound (slow) wave in the ion frame when the relative drifts are large. The unstable waves we consider propagate obliquely to the unperturbed magnetic field and have mixed polarization with significant electromagnetic components. A physical picture of the instability emerges in the limit of a large wave number characteristic of the local approximation. The primary positive feedback mechanism is based on reinforcement of initial electron density perturbations by compression of electron fluid via induced Lorentz force. The resultant waves are qualitatively consistent with the measured electromagnetic fluctuations in reconnecting current sheet in a laboratory plasma.

Received 13 April 2005; accepted 7 June 2005; published 27 August 2005.

Keywords: current-driven microinstability; lower-hybrid drift instability; electromagnetic waves; Whistler waves; magnetic reconnection; anomalous resistivity.

Index Terms: 2772 Magnetospheric Physics: Plasma waves and instabilities (2471); 2723 Magnetospheric Physics: Magnetic reconnection (7526, 7835); 7827 Space Plasma Physics: Kinetic and MHD theory; 7867 Space Plasma Physics: Wave/particle interactions (2483, 6984); 7835 Space Plasma Physics: Magnetic reconnection (2723, 7526).

Full paper: pdf file (300 K b).